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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var stride2offset = require( '@stdlib/strided/base/stride2offset' );
var format = require( '@stdlib/string/format' );
var isMatrixNorm = require( './is_norm.js' );
var base = require( './base.js' );
// MAIN //
/**
* Returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a real symmetric tridiagonal matrix.
*
* ## Notes
*
* - `D` should have `N` indexed elements.
* - `E` should have `N-1` indexed elements.
*
* @param {string} norm - specifies the norm to be returned
* @param {NonNegativeInteger} N - order of the matrix
* @param {Float64Array} D - array containing the diagonal elements
* @param {integer} strideD - stride length for `D`
* @param {Float64Array} E - array containing the sub-diagonal elements
* @param {integer} strideE - stride length for `E`
* @throws {TypeError} first argument must be a valid norm
* @returns {number} norm value
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var D = new Float64Array( [ 4.0, -2.0, 5.0, -1.0 ] );
* var E = new Float64Array( [ 1.0, -3.0, 2.0 ] );
*
* var out = dlanst( 'max', 4, D, 1, E, 1 );
* // returns 5.0
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var D = new Float64Array( [ 4.0, -2.0, 5.0, -1.0 ] );
* var E = new Float64Array( [ 1.0, -3.0, 2.0 ] );
*
* var out = dlanst( 'one-norm', 4, D, 1, E, 1 );
* // returns 10.0
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var D = new Float64Array( [ 4.0, -2.0, 5.0, -1.0 ] );
* var E = new Float64Array( [ 1.0, -3.0, 2.0 ] );
*
* var out = dlanst( 'infinity-norm', 4, D, 1, E, 1 );
* // returns 10.0
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var D = new Float64Array( [ 4.0, -2.0, 5.0, -1.0 ] );
* var E = new Float64Array( [ 1.0, -3.0, 2.0 ] );
*
* var out = dlanst( 'frobenius-norm', 4, D, 1, E, 1 );
* // returns ~8.6023
*/
function dlanst( norm, N, D, strideD, E, strideE ) {
var od;
var oe;
if ( !isMatrixNorm( norm ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid norm. Value: `%s`.', norm ) );
}
od = stride2offset( N, strideD );
oe = stride2offset( N - 1, strideE );
return base( norm, N, D, strideD, od, E, strideE, oe );
}
// EXPORTS //
module.exports = dlanst;
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